\ Visualizing Evolution: October 2008

Thursday, October 30, 2008

Illustrating sauropod hands

From his archives, there's yet another useful post for paleoartists from Tetrapod Zoology:

The hands of sauropods: horseshoes, spiky columns, stumps and banana shapes

It's a great reference and synopsis, and he explains the reasons for the anatomy of the sauropod wrist in context of its evolution from bipedal ancestors (the prosauropods, of which I am painfully familiar).
(from Milàn, J., Christiansen, P. & Mateus, O. 2005. A three-dimensionally preserved sauropod manus impression from the Upper Jurassic of Portugal: implications for sauropod manus shape and locomotor mechanics. Kaupia 14, 47-52.)

I wonder how the wrist structure of the ceratopsians and stegosaurs differ from that of sauropods, given that they also evolved their quadrupedalism separately.

And to the author Darren Naish...
"I also want to note that in no way is it the 'fault' of the artists concerned, given that (1) they've mostly based what they've done on the published work of those who have gone before them, and (2) while many of them have a history of working with palaeontologists, none of the experts they've been advised by before have bothered to tell them what they've been getting wrong."
...I must say thank you! This is so true about science art in any topic, but you could also add that (3) publishers often care more about having a quick deadline than accuracy which forces artists to trust the accuracy of whatever source material and information is given to us.

Now I'm hoping I'll get to do some sauropod work eventually so I can use this good information. The prosauropods I drew for my masters project (See Anatomy: Pages 4 & 5) were bipedal and didn't walk on their hands as adults.

Thursday, October 23, 2008

Linkfest: Sexy Plumage

First, "ask and ye shall receive"! Thanks to everyone who offered and/or sent me a pdf of the nature article in my last post. The pictures look much clearer since I was able to grab them directly from the source! And I promise I'm actually going to read the entire article once I have the time!

Now a couple of links.

Science Crimes: How the Democrats Tried to Destroy Dinosaur Art - you can't make this stuff up. Politicians certainly weren't subtle back in the day.
"Work on the paleozoic museum caught the attention of William 'Boss' Tweed, the notorious figurehead of the city's corrupt Democratic political machine, who denounced the project (there was no apparent graft that could be had from an institution built around collecting fossils). Hawkins, a Londoner raised to believe in the virtue of making public declarations at Hyde Park Corner, held a demonstration in support of the museum during which he openly denounced Tweed. That evening, Tweed's henchmen entered Hawkins's studio and destroyed the dinosaur sculptures."

Early Dinosaur's Feathers Were for Show, Not Flight - A good example for demonstrating that evolution is not goal-oriented. The Jurassic Epidexipteryx couldn't fly, but sported fancy feathers which, like those of a modern peacock, could be used to entice the ladies.
"How YOU doin'?"

Never Say Die: Why We Can't Imagine Death
- Slightly off-topic maybe, but I found this Scientific American article too mind-blowing to not share.
"...the brain is like any other organ: a part of our physical body. And the mind is what the brain does—it’s more a verb than it is a noun. Why do we wonder where our mind goes when the body is dead? Shouldn’t it be obvious that the mind is dead, too?"
Er... and uh, finally, I just noticed that my lovely Coldplay evolution photo has been bumped from the front page, so here it is again, color-balanced to match my blog layout! (Oh god, someone help me!!)

Friday, October 17, 2008

Ubiquity of Branching Structures

These are from an old Nature article The Phenogenetic Logic of Life, Figure 3: Ubiquity of branching structures in living organisms. (Nature Reviews Genetics 6, 36-45 (January 2005))

I can't talk about the actual article because I'm no longer a student with access to the online periodicals, and don't really want to pay the $35 to download the pdf. I'm also going to now resist the very strong temptation to digress into a rant about the cost of online journals and get on to the images. At least I have the captions!

"Multiple applications of branching logic show the logical symmetry of evolution among organisms and development within them."

In other words... visual trees can be used to demonstrate the evolution of organisms, the diversification of cells within an organism, and the resulting anatomical structures of development.

First, two on evolution and speciation:

a. "Charles Darwin's attempt to reconstruct Ernst von Baer's idea that embryos of contemporary similar species, such as vertebrates, have diverged from a common early-embryonic form."

b. "Darwin's sketch of his idea of divergence of species from a common ancestor."

See the original here. I definitely prefer to look at the aged inky version in Darwin's own pen strokes.

The next two are not about evolution, but rather the divergence of cells within a single organism. The patterns that emerge as cell types diversify are similar to those of species diversification:

c. "Divergence of the sequence of a single gene, or members of a gene family, from a common ancestor (the example of photoreceptors and olfactory receptors is shown)."
And similarly:

d. " The divergence of tissues from a single cell within an organism."

Now let's get organismal (is that a word?) and look at branching patterns found in anatomy:
e. "Schematic representation of the fractal-like mammalian bronchial (lung) tree."

And one from the world of botany:

f. "The source of the metaphor — real branches."

$35 ... seriously.

Monday, October 6, 2008

Alligator Genetics and the Development of Bird "Thumbs"

Here is a new article from open-access journal PLoS One: "The Evolution of HoxD-11 Expression in the Bird Wing: Insights from Alligator mississippiensis," (link) which uses color illustrations to explain the genetics and development of the finger digits in birds and alligators. Read the summary on Palaeoblog for a good explanation on the study. Basically, it's a study on Hox genes and how although developmentally birds seem to have digits 2, 3, and 4 from the ancestral 5, this is a result of a "hometic frameshift," causing HoxD-11 expression to move, so ancestrally, their digits are 1, 2, and 3, which is consistent with the fossil evidence such as Archaeopteryx as well as genetic evidence seen in their closest living relatives, the crocodilians.

It's satisfying when evidence adds up in such a neat way.

Anyway, on to the drawings!

Figure 1: Three levels to the avian digit homology problem: embryology, gene expression, and morphology
First of all, the illustrations in this article are just fantastic. Full of information, but designed in a clear way that is in no way overwhelming. There is a didactic use of color, which allows the viewer to follow each of the 5 digits across both development and evolution. The next example includes a more complex clade as well as specific fossil and extant examples.

Figure 2: The evolution of digit morphology

This drawing makes it so easy to compare across the cladogram. You can watch as the digits disappear one by one. I have seen similar illustrations used to show the gradual loss of toes in the evolution of the horse. Janel? You out there? This illustration on Wikipedia is awful! I know there are better ones out there.

And here are the more technical illustrations...

Figure 3: Identification of the alligator
HoxD-11 exon 1 sequence.
Figure 4:The expression of HoxD-11 in alligator and chicken limbs.
I have to admit I often I roll my eyes at the use of photos in lieu of illustrations, but in this case they work amazingly well in tandem. Development is shown in similar stages in alligators and birds, both limbs, and you can trace the development to see where they diverge, and where and which fingers are lost in the bird.